<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>三角形</title>
</head>
<style>
    div {
        width: 0;
        height: 0;
        border-top: 30px solid transparent;
        border-left: 30px solid transparent;
        border-right: 30px solid;
        border-bottom: 30px solid;
    }
</style>

<body>
    <div></div>
</body>
<script>
    function sum(n) {
        if (n === 1) {
            return 1
        } else {
            return n + sum(n - 1)
        }
    }
    console.log(sum(100));
</script>

</html>